1. Field of the Invention
This invention relates to a jet-mixing method and a jet-mixing apparatus for casting piles in soft ground by impregnating the ground with a ground improvement medium, particularly to a jet-mixing method and a jet-mixing apparatus in which a lower first jet nozzle section and a lower second jet nozzle section respectively jet reactant and ground improvement medium in substantially the same direction and an upper third jet nozzle section jets mixed compressed air and water in a direction opposite that of the reactant and ground improvement medium.
2. Description of the Related Art
In building construction and civil engineering, it is a known practice to solidify soft ground before starting the construction work, by impregnating the ground with a ground hardening material. Although various methods have been developed for this type of ground improvement, the jet-mixing method is in particularly wide use because of its operability and reliability advantages.
As taught by Assignee's Japanese Patent Application No. 2003-379126, for example, the conventional jet-mixing method crushes and cuts the ground with water pressure by strongly jetting compressed air and water from a jet nozzle section provided on a rod and then jets and mixes ground improvement medium consisting mainly of cement milk and reactant that promotes hardening of the ground improvement medium, thereby casting a pile of predetermined diameter.
The conventional jet-mixing apparatus comprises a first jet nozzle section and a second jet nozzle section installed so as to spurt material in opposite directions and a third jet nozzle section that jets mixed compressed air and water in opposite directions. So if pile casting is conducted under appropriately set conditions of, inter alia, rotational speed and lifting speed, the ground can be uniformly churned within the required region and a pile of sufficient strength can be quickly formed by adding ground improvement material and reactant.
However, in the jet-mixing method implemented using the conventional jet-mixing apparatus, the reactant and ground improvement medium are jetted in opposite directions owing to the installation of the first jet nozzle section and the second jet nozzle section in opposite directions, and therefore, depending on the ground characteristics and the working conditions, uneven mixing is liable to occur to give rise to cases in which the reactant and ground improvement medium are not properly blended.
A need has therefore been felt for the development of a jet-mixing method and a jet-mixing apparatus that prevent occurrence of uneven mixing and enable reliable blending of the reactant and the hardening material.
Patent Reference 1: Japanese Patent Application No. 2003-379126